1. Technical Field
The techniques described herein relate generally to oscillator circuits, and more specifically to oscillator circuits used for clock and data recovery in an HS-CAN bus system.
2. Discussion of the Related Art
An oscillator circuit produces a repetitive electronic signal. Oscillator circuits are widely used in countless applications. In particular, oscillator circuits may be used in circuits that recover a CAN bus clock. CAN is a multi-master broadcast serial bus standard for connecting electronic circuit devices such as sensors, actuators, and other control devices.
In a CAN network, no clock is sent during data transmission. CAN nodes monitor the CAN bus and handle the bit timing logic (BTL) related to transmission and reception of data. CAN nodes utilize oscillator circuits to recover a CAN bus clock and data.
Evolving standards of the CAN bus, such as HS-CAN, may require CAN bus monitoring with higher accuracy (e.g., 4.5%) and may also increase the frequency of the bus. For example, HS-CAN introduces wake-up frames used to change nodes from a low-power state to an active state. Accurate monitoring is necessary in order to avoid errors such as missing a request to transition from a low-power state to an active state. Further, HS-CAN bus monitoring may increase an oscillator frequency requirement (e.g., 16 MHz).
In order to achieve accurate monitoring, conventional circuits that need to meet high accuracy monitoring requirements may oversample the incoming serial data. The stream may then be evaluated for data transition locations, and valid data bits may then be extracted from the oversampled data. In conventional CAN controller circuits, BTL is generally known to oversample with a frequency much higher than a baud rate in use. In order to oversample, a clock with multiple frequencies much higher than that of the CAN bus is needed.
In order to achieve high accuracy, conventional CAN nodes may incorporate high precision oscillators. Such high precision oscillators may be configured to operate at frequencies considerably higher than the data rate of the CAN bus. High precision oscillators (e.g., quartz, ceramic resonant, etc.) may introduce a higher cost. In addition, operating oscillator circuits at higher frequencies in order to oversample the data is generally known to increase current consumption requirements. Higher current consumption is generally known to be a critical parameter, particularly in HS-CAN transceivers that implement selective wake.